This invention relates to an engine valve assembly, and particularly, to an electromechanical valve assembly for an internal combustion engine.
Automotive manufacturers are currently utilizing camless intake and exhaust valve assemblies to control fluid communication in engine cylinders of internal combustion engines. The camless valve assemblies may utilize hydraulic, pneumatic, or electromechanical means to move a valve.
It is further known that varying an engine valve dwell time (i.e., the time interval a valve is open), a valve dwell position (i.e., the amount the valve is open), a valve opening rate, a valve closing rate, and an initial opening time of a valve (i.e., valve phasing) may be used to increase fuel efficiency and lower emissions. Further, the most flexible valve assemblies may be independently actuated/controlled with respect to other valve assemblies in an engine.
Referring to FIG. 1, a known engine 10 having an engine head 12 and electromechanical valve assemblies 14, 16 is shown. The engine head 12 includes an air intake line 18 and an exhaust line 20. The valve assemblies 14, 16 control communication between the line 18, 20, respectively, with an engine cylinder (not shown).
The valve assembly 14 includes a pair of solenoids 22, 24, and a valve 26. The valve 26 includes a valve stem 28 and a valve head 30. The solenoids 22, 24 are utilized to either open or close the valve 26. In particular, when the solenoid 24 is energized (and solenoid 22 is de-energized), the valve head 30 is moved axially away from a valve seat 32 to allow fluid communication between the intake line 18 and a cylinder (not shown). When the solenoid 22 is energized (and solenoid 24 is de-energized) the valve head 30 engages the valve seat 32 to prevent fluid communication between the intake line 18 and the cylinder. Thus, the known valve assembly 14 has a two-position valve 26 having either a full open state or a full closed state. As such, the valve assembly 14 has several operational disadvantages. In particular, the valve assembly 14 cannot precisely control a valve dwell time duration, a valve dwell position, a valve opening rate, a valve closing rate, valve phasing. Thus, the valve assembly 14 cannot be utilized to effectively increase fuel efficiency and lower emissions in an engine. Further, the valve assembly 14 does not provide for soft seating of the valve head 30 on the valve seat 32 under all operating conditions of the engine 10 including temperature extremes and control strategy variations. As a result, the valve head 30 generates undesirable noise when contacting the valve seat 32.
Another known electromechanical valve assembly (not shown) includes an electric motor, a cam, and a poppet valve. The motor selectively rotates an output shaft that is connected to the cam. The cam converts that rotary motion of the output shaft to an axial motion of the poppet valve. This known valve assembly is capable of controlling a valve dwell time, a valve dwell position, a valve opening rate, and a valve closing rate. However, the known valve assembly suffers from several disadvantages. First, the valve assembly requires a separate cam resulting in increased component and manufacturing costs. Further, the valve assembly requires a relatively large package space since a separate cam is utilized for each poppet valve.
The present invention provides an electromechanical valve assembly for an internal combustion engine.
The electromechanical valve assembly in accordance with the present invention includes a rotor centered about a first axis having a bore extending generally axially therethrough. The valve assembly further includes a stator operatively disposed about the rotor for producing a torque to cause rotation of the rotor about the first axis. Finally, the valve assembly includes a valve having a valve stem and a valve head. The valve stem extends generally axially through the bore of the rotor. The valve is also configured to move generally axially. responsive to the rotation of the rotor to selectively engage and disengage the valve head with a valve seat of the engine. In particular, the valve stem may be threadably engaged with the rotor. Further, the valve stem may have multiple lead engagement with the rotor.
A control system for a linear actuated electromechanical valve assembly is also provided. The control system includes a valve controller for generating a commanded valve position signal to control the incremental axial position of the valve. The valve controller can also vary a valve operational parameter. In particular, the valve operation parameter includes one or more of the following: a valve dwell time, a valve opening rate, a valve closing rate, a valve dwell position, and valve phasing. The control system also includes a position sensor that generates a signal responsive to an axial position of the valve.
A method for current recirculation (i.e., energy recovery) in electromechanical valve assemblies disposed in an internal combustion engine is also provided. The current recirculation methodology is a regenerative method that reduces the energy requirement of electromechanical valves during actuation of the valves. The method includes providing a first electromechanical valve assembly having first and second stator phases selectively connected between a first node and ground. The method further includes providing a second electromechanical valve assembly having third and fourth stator phases selectively connected between the first node and ground. The method further includes generating a braking current in the first and second stator phases of the first electromechanical valve assembly. Finally, the method includes connecting the third and fourth stator phases of the second electromechanical valve assembly to the first node to direct the braking current into the third and fourth stator phases as an accelerating current.
The electromechanical valve assembly and the control system related thereto, represent a significant improvement over conventional valve assemblies and control systems. In particular, the inventive valve assembly and control system enable the precise control of a valve dwell time, a valve opening rate, a valve closing rate, a valve dwell position, and valve phasing. As a result, the inventive valve assembly allows for increased fuel efficiency and lower emissions in an engine as compared with conventional valve assemblies. Further, the position of the valve head may be accurately controlled for soft seating with a valve seat, resulting in reduced engine noise. Still further, the valve assembly may be packaged in a relatively small package volume allowing automotive designers increased flexibility in placement of the engine. Finally, the inventive method of current recirculation provides for decreased electrical energy consumption by the inventive valve assembly as compared with conventional electromechanical valve assemblies.
These and other features and advantages of this invention will become apparent to one skilled in the art from the following detailed description and the accompanying drawings illustrating features of this invention by way of example.